XLPE is the recognized abbreviation for cross-linked polyethylene. This and other cross-linked synthetic materials, of which EPR (ethylene propylene rubber) is a notable example, are being increasingly used as cable insulants for a wide range of voltages.
Polyethylene has good electrical properties and in particular a low dielectric loss factor, which gives it potential for use at much higher voltages than PVC. Polyethylene has been and still is used as a cable insulant, but, as a thermoplastic material, its applications are limited by thermal constraints.
The effect of the cross-linking is to inhibit the movement of molecules with respect to each other under the stimulation of heat and this gives the improved stability at elevated temperatures compared with the thermoplastic materials. This permits higher operating temperatures, both for normal loading and under short-circuit conditions, so that an XLPE cable has a higher current rating than its equivalent PVC counterpart.
The effects of ageing, accelerated by increased temperature, also have to be taken into account, but in this respect also XLPE has favourable characteristics.
BS 5467 specifies construction and requirements for XLPE and EPR-insulated wire-armoured cables for voltages up to 3.3kV. The construction is basically similar to that of PVC cables to BS 6346, except for the difference in insulant. Because of the increased toughness of XLPE the thicknesses of insulation are slightly reduced compared with PVC.
The standard also covers cables with HEPR (hard ethylene propylene rubber) insulation, but XLPE is the material most commonly used. From 3.8kV up to 33kV, XLPE and EPR insulated cables are covered by BS 6622 which specifies construction, dimensions and requirements.